After giving this a little thought, I decided that I did have a pretty good idea on how to do it. It seems you know how to create the DIFF file so I'll just show you how I created a small app that extracts the last part of itself into another file at run time.

No DLLs (other than the standard Windows DLLs) are used in this program. What I've posted here is complete. It does use MFC (which I think is available on your Borland C++ but if not, it should be straightforward to remove all the MFC references.